The invention relates to a ring-like built-up core, of the shape in cross-section of a parallelogram, for the bead of a pneumatic tire for wheel rims with inclined shoulders, the radially-inward surface of the core being inclined in relation to the direction of the axis of the pneumatic tire to be parallel to the bead seat, the wires of the core being trapezoidal in cross-section and disposed side-by-side in lays of wire and being wound in several lays upon a support conically shaped to conform to the inclination of the shoulder of the wheel rim.
As is well known, the bead of a pneumatic tire serves for the sealing of the tire to the wheel rim and for the taking up or transmission of the complex transverse and longitudinal forces occurring.
It is known to manufacture the ring-like built-up core from lays of wire formed of wires of rectangular cross section disposed compactly side by side, several of which lays are wound over one another compactly as the built-up core upon a support which is conical in conformity with the inclination of the wheel rim shoulder. There have been proposed, particularly for pneumatic tires for wheel rims with inclined shoulders, ring-like built-up cores, of the shape of a parallelogram in cross-section, in which the lays of wire are wound compactly over one another in such a way that the radially inward core surface is inclined parallel to the bead seat. (Preliminarily published Federal German Specification No. b 24 10 750). Theoretically, such a ring-like built-up core of the shape of a parallelogram in cross-section with a core inward surface inclined relative to the horizontal can be most easily manufactured from single wires which in cross-section have the shape of a correspondingly matched parallelogram.
In this way there could be formed built-up cores in which all of the individual wires are trued up in the laying direction and superposed vertically. In practice, however, it is found that small individual wires, which in cross-section are of the shape of a parallelogram, are difficult to produce, it being not possible particularly to preserve the necessary tolerances.
It has been found, moreover, that the compact areal superpositioning of the individual wires of the lays of wire is difficult in practice and the cohesion of the built-up core can be compromised by jumping over of individual wires.